The present invention relates to echo-ranging distance determination systems. More particularly, it relates to a system that determines whether a target, such as a vehicle occupant, is located beyond a predetermined distance.
Within a vehicle occupant protection system, it is known to control the inflation profile of an air bag based upon a distance between an air bag assembly and a vehicle occupant. For example, it is known to adjust the amount of inflation fluid provided to an air bag based upon the distance between the occupant and the air bag assembly. The distance between the occupant and the air bag assembly can change during a pre-crash braking condition. Specifically, during a pre-crash braking condition, the vehicle decelerates and the inertia of the occupant causes the occupant to move forward relative to the seat toward an instrument panel that contains the air bag assembly.
A known vehicle occupant protection system includes an echo-ranging system to determine the distance between the air bag assembly and the occupant. The echo-ranging system operates by emitting a short burst of a carrier signal that travels directly between an emitter and the occupant. The emitted signal bounces on the occupant and the bounced signal returns to a receiver as a return echo of the emitted signal. The echo-ranging system includes a time-of-flight distance determination system that determines the time elapsed between the emission of the signal from the emitter and the return of the echo at the receiver, and from this time differential determines the distance between the occupant and the air bag assembly.
Ideally, the time period between signal emission and echo reception is long enough to allow the signal to travel to the occupant and return before the emission of a subsequent signal. However, if the occupant is located sufficiently far away, then the echo returns after a subsequent signal is emitted. Such a return echo can be termed a late echo. Also, although systems are usually designed to bounce the signal on the vehicle occupant, it is possible that the signal may bounce on other surfaces within the vehicle. This situation occurs if the occupant turns or leans and the signal bounces on the occupant""s seat, on a back seat of the vehicle, or on other surfaces within the vehicle. Such other surfaces may also be located sufficiently far to cause return of a late echo.
The result is that the time-of-flight distance determination system calculates the time period between the subsequent emitted signal and the receipt of the return echo (i.e., late echo) associated with the prior emitted signal and thereby miscalculates the distance to be closer than actuality.
One particular type of echo-ranging system includes a head unit that incorporates three ultrasonic transmitters and three ultrasonic receivers for emitting and receiving ultrasonic signals. The system is capable of differentiating between ultrasonic signals generated from transmitters physically separated from each other so that a receiver can identify the source of each ultrasonic signal that is received.
Another type of echo-ranging system is a system that locates the occupant by emitting and receiving ultrasonic signals using two or more ultrasonic transducers. These transducers are located in various locations in the vehicle passenger compartment. As a result, by implementing multiple transducers and by placing each transducer in a different location, each transducer receives the return signal associated with the signal that each individual transducer emitted.
The present invention provides a method and apparatus for determining whether a target is located beyond a predetermined distance. In accordance with one aspect, the present invention provides an apparatus that includes means for emitting first and second signals in an interspersed predetermined emission sequence toward the target. The apparatus includes means for receiving returns of the first and second signals bounced on the target. The apparatus includes means for processing to determine if the target is beyond a predetermined distance using at least one of the returns of the first and second signals and for providing a signal indicative of the determination.
In accordance with another aspect, the present invention provides an apparatus for determining whether a target is located beyond a predetermined distance that includes means for emitting first and second signals in an interspersed predetermined emission sequence toward the target and means for receiving return echoes of the first and second signals.
The apparatus includes means for successively determining a time interval between the emission of a current signal and the reception of an echo. The apparatus further includes means for successively comparing at least two time intervals to determine whether a sufficient difference exists to indicate that the target is beyond the predetermined distance and for outputting a signal indicative thereof.
In accordance with another aspect, the present invention provides an apparatus for determining whether a target is located beyond a predetermined distance that includes means for emitting first and second signals in an interspersed predetermined emission sequence toward the target and means for receiving returns of the first and second signals bounced on the target.
The apparatus further includes means for controlling said means for emitting the first and second signals to overlap a first time-of-flight period of the first signal, wherein the first time-of-flight period occurs between emission and echo reception of the first signal, and a second time-of-flight period of the second signal, wherein said second time-of-flight period occurs between emission and echo reception of the second signal. The apparatus includes means for successively determining a time interval between the emission of a current signal and the reception of an echo. The apparatus further includes means for performing a distance calculation to the target using at least one of the time-of-flight periods of the first and second signals and for outputting a signal indicative thereof.
In accordance with still another aspect, the present invention provides a method that includes the steps of emitting first and second signals in an interspersed predetermined emission sequence toward the target and receiving returns of the first and second signals bounced on the target. The method also includes the step of processing to determine if the target is beyond a predetermined distance using at least one of the returns of the first and second signals, and providing a signal indicative of the determination.
In accordance with another aspect, the present invention provides a method for determining whether a target is located beyond a predetermined distance that includes the steps of emitting first and second signals toward the target in a staggered emission sequence and receiving return echoes of the first and second signals.
The method further includes the steps of successively determining a time interval between the emission of a current signal and the reception of an echo and successively comparing at least two time intervals to determine whether a sufficient difference exists to indicate that the target-is beyond the predetermined distance and outputting a signal indicative thereof.
In accordance with another aspect, the present invention provides a method for determining whether a target is located beyond a predetermined distance that includes the steps of emitting first and second signals in a staggered emission sequence toward the target and receiving returns of the first and second signals bounced on the target. The method includes the step of controlling said step of emitting the first and second signals to overlap a first time-of-flight period of the first signal, wherein the first time-of-flight period occurs between emission and echo reception of the first signal, and a second time-of-flight period of the second signal, wherein said second time-of-flight period occurs between emission and echo reception of the second signal.
The method further includes the steps of successively determining a time interval between the emission of a current signal and the reception of an echo, successively comparing at least two time intervals to determine whether a sufficient difference exists to indicate that the target is beyond the predetermined distance and outputting a signal indicative thereof. The method further includes the step of performing a distance calculation to the target using at least one of the time-of-flight periods of the first and second signals and outputting a signal indicative thereof.